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1, 16 • Drilling of one soil boring (B-1 to 81.5 feet) and one monitoring well (MW-4 to 95 feet) by a Remediation Services, Inc (RSI) subsidiary, BSK & Associates (BSK), in October 1992 • Drilling of four soil borings (B-101 to 75 feet, B-102 to 75 feet, B-103 to 75.5 feet, and B-104 to 75 feet) by BSK in February 1993 • Installation of two monitoring wells (MW-5 to 90 feet and MW-6 to 89 feet) by BSK in December 1993 • Excavation of approximately 330 cubic yards of petroleum-impacted soil from the former UST pit and vicinity by IT in May 1995 A vapor observation point was constructed at the base of the excavation The excavation was subsequently backfilled with clean Imported fill material and capped • Drilling of two soil borings to 64.5 feet (SB-1 and SB-2) by IT in August 1995 • Fourteen quarterly groundwater monitoring events by BSK and IT since October 1992 t Figure 2 provides a site plan Multiple site investigations have confirmed only TPH as diesel g Y In soil and groundwater Consequently PHS/EHD has recommended that only the mass loading of residual TPH as diesel to the groundwater be modeled 3.0 VL EA CHSM Mode! VLEACHSM was released In May 1995, by the USEPA Kerr Environmental Research Laboratory It uses a one-dimensional finite difference scheme to estimate the migration of an organic contaminant (TPH as diesel, in this case) through the vadose zone and a mass- balance technique to estimate the concentration of a contaminant in the saturated zone following the mixing of leachate from the vadose zone with groundwater In order to conservatively calculate the maximum potential impact to the groundwater, the saturated zone mixing module was not run Instead, leachate calculated to arrive at the groundwater Interface was assumed not to mix with groundwater This provided a highly conservative, "worst-case" estimate of Impact to the groundwater MZ/11-0 1-96/VDBF/96-0022 LF 2